In the mammalian heart, the tricuspid valve separates the right atrium and right ventricle and prevents backflow of blood from the right ventricle into the right atrium during contraction. The left atrium and left ventricle are separated by the mitral valve, which, similar to the tricuspid valve, prevents backflow of blood into the left atrium when the left ventricle contracts.
Regurgitation (leakage) of the mitral valve or tricuspid valve can result from many different causes, and can cause heart irregularities, such as an irregular heart rhythm, and itself can cause inexorable deterioration in heart-muscle function. Such deterioration can be associated with functional impairment, congestive heart failure and significant pain, suffering, lessening of the quality of life, or even death. Mitral valve regurgitation (“MR”) is broadly categorized as either organic or secondary (i.e. functional). With organic MR, there is a primary structural abnormality of the mitral valve resulting in improper coaptation of the valve. The most common causes of organic MR include degenerative disease, rheumatic valve disease, endocarditis with leaflet destruction, and congenital mitral valve disease. With secondary MR, the leaflet structure is largely preserved and regurgitation is caused by a dilated annulus and/or subvalvular traction impairing leaflet apposition.
Pharmacologic treatments for valvular regurgitation generally include diuretics and vasodilators. These medicines, however, have not been shown to alter the natural progression of cardiac dysfunction associated with regurgitant valves.
Cardiac resynchronization therapy (biventricular pacing) has value as a non-surgical option in “functional” or secondary mitral valve regurgitation.
Surgical options for correcting defects in the heart valves include repair or replacement of a valve, but these surgical options require open-heart surgery, which generally requires stopping the heart and cardiopulmonary bypass. Recovery from open-heart surgery can be very lengthy and painful, or even debilitating, since open-heart surgery requires pulling apart the ribs to expose the heart in the chest cavity. Cardiopulmonary bypass itself is associated with comorbidity, including cognitive decline. Additionally, open-heart surgery carries the risk of death, stroke, infection, phrenic-nerve injury, chronic-pain syndrome, venous thromboembolism, and other complications. In fact, a number of patients suffering heart-valve defects cannot undergo surgical-valve treatment because they are too weak or physiologically vulnerable to risk the operation. A still larger proportion of patients have mitral-valve regurgitation that is significant, but not sufficiently so to warrant the morbidity and mortality risk of cardiac surgery.
Percutaneous approaches to valve repair have been developed to reduce the clinical disadvantages of the open-heart procedures. In some percutaneous techniques, a prosthesis is advanced in a catheter through the subject's vasculature to the vicinity of the mitral valve. These percutaneous techniques are attractive alternatives to conventional surgical treatment because they do not require open heart surgery or extracorporeal circulation, and can be used in a closed chest and beating heart. The treatment is potentially less morbid and can be applied to a wider range of patients including those with less severe valvular dysfunction.
Examples of percutaneous valve repair procedures include coronary-sinus shortening devices, transcameral fixtures, endoventricular annular plication, and direct leaflet stapling. Coronary sinus annuloplasty techniques have been disclosed, for example, in U.S. Pat. Nos. 6,402,781 and 7,090,695. However, these techniques have shown only limited success in establishing circumferential tension that characterizes effective surgical ring annuloplasty. For example, in mitral valve repair, the sinus-shortening devices have induced only local shortening across the mitral commissures but do not adequately reduce the septal-lateral separation that characterizes functional mitral valve regurgitation. The leaflet procedures have not been able to reduce annular dilation and they can also impair the normal dynamic line of mitral valve coaption that accommodates a range of volumes and inotropic states.
A more recent improvement of percutaneous annuloplasty is percutaneous cerclage annuloplasty or coronary sinus transcatheter-mitral-valve cerclage annuloplasty, which is disclosed, for example, in U.S. Published Patent Application Nos. 2005/0216039 and 2010/0049314. This technique involves the introduction of tensioning material around the mitral-valve annulus using a secondary catheter, such as a steerable guide wire or canalization catheter. Access to the area around the mitral-valve annulus can be accomplished using a number of different percutaneous approaches, including access from and through the coronary sinus. For example, a continuous strand of tensioning material such as a ligature is applied around the mitral-valve annulus along a pathway that includes an extraanotomic portion. For example, the tensioning material can traverse a region between the anterobasal-most portion of the coronary sinus and the coronary-sinus ostium. In another approach, a tensioning material is applied across the atrial aspect of the mitral valve from the posterolateral aspect to the anterior aspect of the coronary sinus, or from the septal aspect to the lateral aspect of the mitral-valve annulus. By such cerclage techniques, the mitral annular cross-sectional area is reduced, including a reduction in septal-lateral wall separation, thereby intrinsically reapposing the line of coaptation of the mitral valve. During such techniques, the tensioning material can be placed with the assistance of imaging technologies that may include X-ray fluoroscopy, magnetic resonance imaging, intracavitary or external ultrasound, electroanatomic mapping, X-ray computed tomography or a combination (fusion) of any of these imaging technologies.
While percutaneous cerclage annuloplasty is a promising technique for valve repair, enhancing valve leaflet coaptation, and treating valve regurgitation, the procedure is technically demanding and requires great skill and precision in positioning the tensioning system to provide the proper plane of cerclage. Further, entrapment of tricuspid valve subvalvular structures, such as trabeculae or chorda tendinea or of ventricular structures such as the moderator band and non-valvar trabeculae, is an important limiting adverse consequence of the cerclage procedure that requires great skill, effort and prolonged procedures to avert. Entrapment occurs when a cerclage traversal catheter system undermines a trabecular or other subvalvar element while it passes from an intramyocardial trajectory into the right ventricular cavity. In the event that such entrapment is not averted, the subvalvar or trabecular structures may become entrapped or transsected, and the tricuspid valve or right ventricle may be irreversibly damaged causing procedural failure and serious adverse consequences. Therefore, a need exists for improved techniques and devices that facilitate proper positioning of the tensioning system during such demanding and complex cerclage procedures and, further, which can prevent trabecular entrapment.